1. Field of the Invention
The present invention relates generally to wireless communications, and more particularly to a system and method for accessing a multi-line gateway using cordless telephony terminals.
2. Discussion of the Related Art
In today's electronically interconnected world, the normal complement of electronic equipment in the home or business includes devices that are connected to one another in different ways. For example, many desktop computer systems have a central processing unit (CPU) connected to a mouse, a keyboard, a printer and so on. A personal digital assistant (PDA) will normally connect to the computer with a cable and a docking cradle. A television may be connected to a VCR and a cable box, with a remote control for all three components. A cordless phone connects to its base unit with radio waves, and it may have a headset that connects to the phone with a wire. In a stereo system, a CD player, tape player and record player connect to a receiver, which connects to speakers. These connections can be difficult to install and maintain, particularly for the lay user.
Alternatives to these conventional approaches to connectivity have been proposed. Bluetooth™ (BT) is a computing and telecommunications industry specification for connectivity that is both wireless and automatic, as described in The Specification of the Bluetooth System, Version 1.1, Feb. 22, 2001, (“the BT specification”), which is incorporated herein by reference. BT allows any sort of electronic equipment—from computers and cell phones to keyboards and headphones—to make its own connections, without wires, cables or any direct action from a user. Because BT connections are wireless, offices can be designed without regard to cable placement and users can travel with portable devices without having to worry about carrying a multitude of cables. These connections can be established automatically, where BT devices find one another and form a connection without any user input at all.
BT requires that a low-cost microchip transceiver be included in each device. The BT microchip transceiver communicates on a frequency of 2.45 GHz, which has been set aside by international agreement for the use of industrial, scientific and medical devices (ISM). In addition to data, up to three voice channels are available. Each BT device has a unique 48-bit device address from the Institute of Electrical and Electronics Engineers 802 standard. Connections can be point-to-point or multi-point. Data can be exchanged at a rate of 1 megabit per second (up to 2 Mbps in the second generation of the technology).
A number of common consumer devices also take advantage of the same radio frequency (RF) band. Baby monitors, garage-door openers and some cordless phones all make use of frequencies in the ISM band. The BT design employs various techniques to reduce interference between these devices and BT transmissions. For example, BT avoids interfering with other systems by sending out relatively weak signals of 1 milliwatt. By comparison, some cell phones can transmit a signal of 3 watts. The low power limits the range of a BT device to about 10 meters, thereby reducing the probability of interference with other devices.
BT also employs a spread-spectrum frequency hopping scheme to further reduce interference and increase capacity. BT devices use 79 randomly chosen frequencies within a designated range, changing from one to another on a regular basis 1,600 times every second. The random frequency hopping pattern makes it unlikely that two BT transmitters will be on the same frequency at the same time, thus reducing the probably of BT devices interfering with one another. This technique also minimizes the risk that other non-BT devices such as portable phones or baby monitors will disrupt BT devices since any interference on a particular frequency will last only a fraction of a second.
When BT devices come within range of one another, an electronic conversation takes place to determine whether they have data to share or whether one needs to control he other. Once the conversation has occurred, the devices form a “piconet”. A piconet ay link devices located throughout a room, such as a home entertainment system, or devices much closer together such as a mobile phone on a belt-clip and a headset, or a computer, mouse, and printer. Once a piconet is established, the connected devices randomly hop frequencies in unison to communicate with one another and avoid other piconets that may be operating nearby.
One device acts as the master of the piconet, whereas the other unit(s) acts as slave(s). Up to seven slaves can be active in a single piconet. The slaves synchronize to the master's timing, and access to the channel is controlled by the master. The channel is represented by a pseudo-random hopping sequence hopping through the 79 RF channels. The hopping sequence is unique for each piconet and is determined by the BT device address of the master, the phase in the hopping sequence is determined by the BT clock of the master. The channel is divided into time slots where each slot corresponds to an RF hop frequency. Consecutive hops correspond to different RF hop frequencies. The nominal hop rate is 1,600 hops/second. All BT devices participating in the piconet are time- and hop-synchronized to the channel.
Between master and slave(s), different types of links can be established. Two link types have been defined in the BT specifications: Synchronous Connection-Oriented (SCO) links, and Asynchronous Connection-Less (ACL) links. The SCO link is a point-to-point link between a master and a single slave in the piconet. SCO links support real-time voice traffic using reserved bandwidth. The ACL link, by comparison, is a point-to-multipoint link between the master and all the slaves participating on the piconet. In the slots not reserved for SCO links, the master can exchange packets with any slave on a per-slot basis. The ACL link provides a packet-switched connection between the master and all active slaves participating in the piconet.
Data on the piconet channel is conveyed in packets. Each packet consists of three entities: the access code, the header, and the payload. The access code and header are of fixed size: 72 bits and 54 bits respectively. The payload can range from zero to a maximum of 2745 bits. Packets may include the access code only, the access code header, or the access code header payload. In an ACL link, the master can either broadcast packets to every slave in the piconet, or send packets to a particular slave. ACL packets not addressed to a specific slave are considered as broadcast packets and are read by all the slaves. In the reverse direction, the master controls slave access to the channel.
As mentioned above, BT wireless techniques can be applied to a number of environments. One such environment is cordless telephony. The Cordless Telephony Profile (CTP) portion of the BT specification, for example, describes a “3-in-1 phone” wherein an extra BT mode of operation is provided to cellular phones. The 3-in-1 phone uses this BT mode as a short-range bearer for accessing fixed network telephony services via a base station. The CTP describes various protocols for handling voice and data transmissions between the base station, referred to in the specification as a gateway, and a small number (maximum 7) of terminals. The gateway provides access to an external network, such as a public switched telephone network (PSTN). However, the techniques described in the CTP can also be applied generally for wireless telephony in a residential or small office environment, such as for cordless-only telephony or cordless telephony services in a personal computer (PC).
The CTP covers various scenarios, such as connecting to the gateway so that incoming calls can be routed to the terminal and outgoing calls can be originated, making a call from a terminal to a user on the external network, receiving a call from the external network, and making direct calls between two terminals. The CTP describes the gateway having a single line connecting the gateway to the external network. Procedures are described for handling calls received on this single line. This simple gateway will provide sufficient functionality for many environments, such as for personal use in a home having a single phone line.
However, many environments require that gateways support multiple lines coming from the external network. In this scenario, the terminals and gateway should be able to handle simultaneous calls on multiple lines. The CTP does not provide for this multi-line support. This limitation results, at least in part, from the terminal's inability to distinguish signaling information associated with calls that are occurring simultaneously. Signaling information is transmitted as packets of data As defined in the BT specification, these packets do not contain a field for identifying a particular call with which the packet is associated. This does not pose a problem when handling at most a single call at any given time, because the terminal assumes that all signaling information is associated with the single call. Problems arise, however, when packets associated with simultaneous calls arrive at the terminal. The packets do not identify themselves with a particular call, and the CTP does not describe using any other mechanism for making this association. The terminal is therefore unable to handle the signaling associated with multiple calls.
Furthermore, the CTP does not describe how terminals might access data stored at the gateway, nor does the CTP describe how data can be accessed while simultaneously handling a call. In many scenarios, data of interest to users could be stored by the gateway, such as phone book data, directories, and lists of phones calls made or received. Making this information available at the terminal requires that the stored data be transferred from the gateway to the terminal. The CTP does not describe procedures for accomplishing this transfer. There also could be situations where the user might wish to access this information during a call. For example, a user during a phone call might want to provide a phone number to another party on the call. It would be helpful if the user could access conveniently the stored phone book data using the terminal, and then read the desired number to the other party. The CTP does not describe how to access data while simultaneously handling a phone call.
What is needed therefore is an improved system and method for supporting calls on multiple lines in a cordless telephony environment. Further, there is also a need for an improved system and method for accessing data stored at the gateway, particularly where the access occurs during a call.